IF7 is one type of gas useful for etching in a semiconductor production process or for cleaning in nuclear industry. For example, Japanese Laid-Open Patent Publication No. 2009-23896 describes using IF7 or IF5 as gas for etching or cleaning in a semiconductor production process. Generally in an etching process using IF7, the utilization factor of IF7 is as low as 5 to 20%, and a most part of IF7 is discharged as exhaust gas. However, such a fluoride discharged into the atmosphere promotes global warming. In addition, iodine occupies a high ratio of production cost of IF7. For these reasons, it is desired to recover and reuse IF7.
As a method for recovering a fluoride from exhaust gas, Japanese Laid-Open Patent Publication No. Hei 9-129561, for example, describes a method of cold-trapping fluorine-based gas by use of a cold trap that uses low-boiling point inert gas (liquid nitrogen, liquid argon, etc.) as a coolant. However, unlike other fluorides, IF7 needs a very low temperature of about −200° C. to be recovered by cold-trapping, and it imposes a great load on the device to keep such a low temperature. In addition, IF7 easily sublimates at a low pressure as in the semiconductor process. Therefore, use of a generally used cold trap having a temperature of about −30 to −80° C. decreases the recovery ratio.
Japanese Laid-Open Patent Publication No. 2000-117052 describes a method of recovering a fluoride free of impurities by adsorbing the fluoride to a specific adsorbent such as activated carbon or the like and desorbing the fluoride by heating. However, it is difficult to refine and reuse IF7 by use of such an adsorption and desorption method because unlike other fluorides, IF7 is easily reactive with an adsorbent such as activated carbon, zeolite or the like.
Japanese Laid-Open Patent Publication No. 2011-5477 describes a method of reacting iodine fluoride with an agent such as soda lime or the like to detoxify the iodine fluoride. Since iodine fluorides such as IF7, IF5 and the like are costly, it is not economical to detoxify exhaust gas generated after etching by use of a wet or dry detoxification device.